This invention relates to a telecommunications network including a channel switching protection arrangement and in particular relates to a way of identifying a channel, section, path or the like so that it can be switched remotely in an SDH (Synchronous Digital Hierarchy) network.
Conventionally in SDH the term "section" is associated with the physical links between adjacent nodes in a network, while the term "path" is associated with a communication link between a pair of nodes, wherever they are located in the network. Each section and path is uniquely identified in SDH by a so called section or path trace signal respectively which has in the past been used as a means of checking that a traffic signal arriving at a particular node is the correct one and for raising an alarm signal if it is not. As used within the specification the term "channel" will be used to describe either a path or a section, the important factor being that each channel, path or section connecting a pair of nodes is uniquely identified by means of a trace signal.
SDH, and the similar North American SONET (Synchronous Optical Network) system, provide a number of protection strategies including Multiplex Section and Path Protection. These strategies provide an adequate means for supporting a 1+1 or 1:1 architecture (i.e. those where one protection path or section serves one working path or section). However a 1:n architecture (i.e. where one protection path or section serves n working paths or sections) is of limited use in Multiplex Section Protection and is not provided for at all by Path Protection.
Multiplex Section Protection (MSP) provides a means of protecting the STM-N (Synchronous Transport Module)/STS-n (Synchronous Transport Signal) signal against channel-associated failures within the multiplex section. A protocol is supported by the K1/K2 bytes and as such provides for either linear protection switching between two adjacent sites or ring switching where the protection between two adjacent sites has also failed.
Path Protection provides a means of protecting the VC-n (Virtual Container)VT-n (Virtual Tributary) signal against channel associated failure within the higher-order/lower-order path respectively. A protocol has been proposed that will support a 1+1 or 1:1 switching only and in its present form could never support a 1:n architecture due to the vast amount of paths present at any one node and as such in the entire network.